It’s important to point out that either pilot can command the 505 to “Fly,” but both pilots have to command it to “Idle.”
It sounds safeguarded well enough in principle, but humans can mess things up.
In practice:
During training, the one doing powered maneuvers has their collective throttle switched to the “Fly” position, with the other switched to the “Idle” position. The aircraft was designed so that only one throttle is switched to the ‘Fly’ position,
However, for teaching full touchdown autorotations, the student has his throttle switched to “Idle,” and the instructor’s is in the “Fly” position. This way the instructor is in charge of going to “Idle” to start the maneuver, and he has ultimate control to go back to powered flight if necessary.